This invention reltes to a peak demand limit controller and, more specifically, to a controller to reduce the power consumption of condition controlling loads in order to prevent power consumption of a building's loads from exceeding a predetermined demand limit.
In the recent past, demand for electrical energy has exceeded supply, particularly during seasonal peak load periods. For example, during the summer cooling season, suppliers of electricity have been unable to supply sufficient energy to satisfy their customers on those hot and humid days when both residential and industrial customers are drawing heavily upon the electrical supply to air condition their buildings. In some areas of the country, the desparity between the available supply of electricity and the demand for that electricity, during seasonal peak load periods, have caused "brown-outs" where the electricity supplied to customers is materially reduced because of high customer usage and "black-outs" where that usage is so high that it causes malfunctioning of the electrical generating equipment.
In order to avoid the high cost of constructing additional electrical generating plants to meet demand during seasonal peak load periods, suppliers charge a penalty whenever a user's power consumption exceeds a predetermined level. To avoid being charged these penalties, users have attempted to limit power consumption during seasonal peak load periods by cycling fans on and off or by limiting compressor capacity whenever the power consumption of the building approaches a predetermined demand limit, as established by the power company, and above which the penalty is charged.
However, cycling fans on and off produce space upsets, i.e., wide temperature fluctuations, increase equipment wear and preclude load reset of the chiller plant. Limiting chiller capacity has a number of drawbacks. All loads are similarly affected such that heavy loads are penalized most and light loads are not affected. Pumping power is increased because the chilled water temperature rises and local loop control, as a result, calls for increased flow. Also, the chilled water temperature is raised which impairs the dehumidification capability of the system.